The present invention pertains to a process and to a device for coordinating in good register cylinders of a web-fed rotary printing press which print on a web.
The ability to change over from one production to the next as rapidly as possible and with the smallest possible amount of waste as possible plays an increasing role in web-fed rotary printing. Newspapers and journals are increasingly tailored to the local needs or to certain target groups, so that even though the number of editions increases, the volume of the individual editions decreases. The significance of production change increases to achieve economy of the printing press.
Designs of printing presses which can be configured in a flexible manner and at the same time contribute to keeping the purchase cost low despite increased flexibility, have been known from the applicant""s EP 0 644 048 A2. The designs of the individually driven print positions described there for rubber/rubber and steel/rubber productions make possible a flying plate change during continuous production. Printing cylinders that are not needed in the current production are moved on and up during the running production here and are brought into contact with counterpressure cylinders when a preset circumferential velocity is reached, so that the new print positions are formed for the next production. The new printing positions or printing gaps, which are formed between two cylinders printing on the web, i.e., between printing cylinders, are on the path of the web of the still running production. The web does not have to be pulled in again. Cylinders of print positions of the still running production which are no longer needed are pivoted away. The new production begins and joins the preceding one in a seamless manner. It is no longer necessary with these prior-art printing presses and printing press designs to bring the press to a stop at the time of a change in production and to start it up from the stop, so that the changeover times can be considerably reduced, in the ideal case to zero.
In flying plate change, e.g., in the case of changes in the web width, and the flying production change made possible by it, the circumferential velocity of the printing cylinders for the preceding old production is first reduced in most cases to a preset value, e.g., to 30% of the velocity occurring in the production run, and the new cylinders are engaged with their counterpressure cylinders after the same circumferential velocity has been reached. The new production is assumed at this velocity. The cylinders that now form the print positions are subsequently accelerated to the velocity of the production run. In the case of a change in production, two velocity ramps are thus passed through in this case. The drive design of the printing presses described in the above-mentioned documents with individually driven printing units also makes it possible, compared with the previously usual drives with a common shaft, a considerably more rapid passage through the velocity ramps, so that the changeover times between two productions can be reduced even more.
The primary object of the present invention is to improve the registry and consequently the quality of the printed image on a printed web.
This object is accomplished by printing on one side of the web with first and second cylinders. The cylinders are driven with first and second motors, where motor controllers are used for maintaining preset angular positions of the first and second cylinders. A disturbance variable (v) is sent to a command variable (u2.Soll) for the motor controller the second cylinder to compensate a register deviation (Y12) of the second cylinder from the first cylinder. The register deviation being typical of the disturbance variable (v).
The present invention is based on web-fed rotary printing presses, especially the offset printing of newspapers, as they have been known from, e.g., EP 0 644 048 A2. A first cylinder printing on one side of a web is driven by a first motor, and a second cylinder printing on the same side of the web is driven by a second motor, i.e., there is no mechanical coupling between the first and second cylinders for a common drive by a common motor. The two motors are not connected in a positive-locking manner for purposes of drive. Both motors are controlled with respect to the angular position of the cylinders driven by them.
A disturbance variable is sent according to the present invention to the motor controller of the motor for the second cylinder. Major deviations in the circumferential register, i.e., register errors or register deviations which would otherwise occur without such an additional sending are counteracted by the additionally sent disturbance variable. The circumferential velocity of the cylinder or a variable from which the circumferential velocity can be determined is preferably used as the disturbance variable. The circumferential velocity or the equivalent variable is preferably measured at each of the cylinders and is sent to that cylinder or is measured representatively for the cylinders to be coordinated with one another in good register at one of these cylinders and is sent to each of the other cylinders. A control member forms from this a disturbance variable that is to be sent based on a stored, velocity-dependent characteristic.
Thus, even though the angular position of the cylinders is conventionally controlled and regulated in terms of a synchronous run during the passage through velocity ramps and also during the production run, the accidental and foreseeable changes in the behavior of the web during the operation are not taken into account. For example, the pull of the web is a function, among other things, of the velocity of the web. Such changes in the behavior of the web, which also occur especially during nonstationary operation and cause intolerable register errors, are compensated by the sending according to the present invention of an additional disturbance variable to the setting variable of the register controller or directly to the command variable for a motor controller or they are not allowed to occur in the first place. Each of the motors is thus controlled on the basis of the conventional command variable, e.g., the absolute angular position. At least the motor for the cylinders to be coordinated is, moreover, controlled on the basis of the additionally sent disturbance variable to compensate a foreseeably changing web behavior.
The disturbance variable, which is to be sent at discrete times or continuously, especially during the passage through velocity ramps, may be determined empirically or by simulation or a combined method.
In the case of an empirical method, all the velocity ramps that can be planned and are possible during the later operation are passed through for the given type of press. The printed copies produced in the process can be delivered and the register marks can be measured. The velocity ramps are passed through in steps, such that one passes over into production run at preset times during a phase of acceleration or deceleration at the cylinder circumferential velocity just reached and the register marks thus printed are measured and evaluated. This procedure is followed at each step of the velocity ramp. Discrete values for register errors and register deviations are obtained from the evaluation, and the values for the disturbance variable to be additionally sent, with which the register error, which would otherwise occur without the sending of the disturbance variable, is compensated, are determined from these. Interpolation is possible between the discrete values obtained by this manner of measurement for the register deviation, and a continuous, preferably constant curve of the register deviation over the circumferential velocity of the cylinder can be obtained as a result. However, the disturbance variable may also be sent in discrete steps.
The ink register-measuring devices present in the press for automatic measurement are advantageously used for this purpose in the case of the empirical method.
The empirically found relationship may be used to send the disturbance variable when passing through velocity ramps during the later operation.
A process especially suitable for determining the register error in conjunction with a mark that is also especially suitable for the present invention, with which the register error can be determined, among other things, is described in the applicant""s German Patent Application No. 196 39 014.1, whose disclosure is herewith referred to for the purposes of the present invention.
In an advantageous variant, the control behavior of at least the register controller for the second cylinder is changed specifically when a change that affects the circumferential register is made in a production condition. The change in the control behavior is brought about by making a specific change in at least one controller parameter. Changes in production conditions which induce a change according to the present invention in the control behavior are changes whose effect on the circumferential register or on the registry is foreseeable and reproducible. These include especially a change in the web length between two adjacent print mechanisms and optionally also to the sensors picking up the register as a consequence of a transformation of print positions and/or a change in the velocity of the web, especially during phases of acceleration and deceleration and/or a change in the paper grade as a consequence of a roll change and/or a change in the ink and moisture supply.
The preferred response to one or more changes in production conditions consists of an adapted change in the control behavior of the controller, namely, a controlled adaptation of at least one controller parameter, optionally of all or at least all essential controller parameters. The setting of the controller is adapted to the changed situation in real time or in an anticipating manner, preferably partly in real time and partly in an anticipating manner. As a real time variable, the formation of the controller parameter preferably includes the circumferential velocity or the velocity of the cylinders to be coordinated in good register. However, it is also possible to use, instead, the circumferential velocity of one of the other cylinders, which are to be coordinated with the second cylinder in good register, e.g., that of a reference cylinder.
In particular, changed web paths and web lengths that have changed as a result of such a change are taken into account in an anticipating manner by reading in parameter basic values at the time of the change in production.
In a device according to the present invention for coordination in good register, a control member is provided at least for the second cylinder to be coordinated in good register with the first cylinder, wherein the said control member forms a correction variable for compensating a register deviation of the second cylinder from the first cylinder, which register deviation is typical of the disturbance variable, from a disturbance variable, especially the circumferential velocity of the cylinder to be coordinated or of one of the other cylinders printing on the same side of the web.
The control member preferably has a memory, in which the disturbance variable-dependent curve of the register deviation of the second cylinder from the first cylinder is permanently stored or is read in for the particular case of printing by a higher press control or is selected from a plurality of permanently stored curves.
In an advantageous variant of the device, a register controller for the second cylinder to be coordinated with the first cylinder has a preferably digital signal processor, with a separate memory, in which the parameter basic values for the controller parameters of this controller are stored or into which the particular valid parameter basic values can be written. If a read-only memory is used, the circuit or the signal processor of the controller needs only be told which of these stored basic values shall apply to the current case of operation for the particular controller parameter. In one exemplary embodiment, the controller itself has both a RAM and a ROM and it receives the information from a higher control via a control signal only on which value or data set stored in the ROM of the controller it shall take over into its RAM and use it for the time being. However, the current set of values for the controller parameters may also be loaded directly into a RAM of the controller from the higher control.
In another advantageous embodiment of the present invention, a partial control system including a third cylinder is uncoupled from a partial control system including the second cylinder in terms of the circumferential register. The third cylinder prints on the same side of the web as do the first and second cylinders and it follows the second cylinder when viewed in the direction of travel of the web.
In a multicolor printing press, on which the present invention is preferably based, the first cylinder prints the reference color, and the second and third cylinders are coordinated with the first cylinder in good register. Changes in the cylinder position of the preceding cylinder or cylinders are passed on by uncoupling members in the register controller to the drive controller of the third cylinder as a change in the cylinder position such that the effect on the web tension is compensated by a register correction performed at the second cylinder or at the first and second cylinders.
The features disclosed above can be used not only for regulating or controlling the cylinders that are to be coordinated with a cylinder printing the reference color in good register. The cylinder printing the reference color itself may be regulated and/or controlled in the same way. This is advantageous for printing in good register, e.g., if there is a common component in the setting variables of the register controllers of all the printing inks following the reference color.
The described control and optionally regulation of the circumferential register may advantageously also be used for controlling and optionally regulating the crop mark, i.e., the register controllers of the cylinders can also be adapted in a controlled manner with respect to the crop mark. The crop mark may be taken into account in the course of the sending of the disturbance variable, advantageously with, but also without controlled adaptation.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.